The proposed research seeks to obtain fundamental structural and kinetic information about the ways in which certain toxic metal species, present as contaminants in the environment, interact with biomolecules. The interactions considered are basic to the toxicology of trace metals and relate to: the inhibition of sigma-aminolevulinic acid dehydratase by Pb in imparing heme synthesis; the role of metallothinein in storing Cd in the kidney; enzyme inhibition by Cd-Zn exchange in the representative enzyme aspartate transcarbamylase from E. coli.; and the factors affecting trans-membrane transport of inorganic and organic species of Pb, Cd, Hg, T1, As, Se and Be across membranes. NMR spectroscopy of H1, C13, P31, C135 and Cd113 nuclei will be employed to determine both structural and kinetic information at the molecular level. Dual wavelength electronic spectroscopy is extensively employed to determine stability constants for interactions between metal ions and biomolecules using the complexing dye, Murexide, as a competing ligand.